Shatterproof (The 39 Clues: Cahills vs. Vespers #4)

After seven of their relatives were kidnapped, Amy and Dan Cahill scoured Europe for the priceless artifacts Vesper One demanded in exchange for the hostages. The Cahill kids are given an assignment that pushes them to a journey to a legendary city. Amy and Dan can't afford to fail, yet they're running out of options and time. With the body count rising, the hostages are pushed to desperate measures that will either change the game - or eliminate some of the players forever.